Back lighted electrostatic copyboard



United States Patent [72] Inventor Dolph Simons Philadelphia, Pa.

[21 Appl. No. 737,400

[22] Filed June 17, 1968 [45] Patented Dec. 22, 1970 [73] Assignee The Simco Company, Inc.

Lansdale, Pa.

a corporation of Pennsylvania [54] BACK LIGHTED ELECTROSTATIC COPYBOARD 12 Claims, 3 Drawing Figs.

[52] US. Cl. 317/262 [51] Int. Cl. H05X G02b [50] Field ofSearch 317/262:

250/lnquired: 40/ 106. 1. 341 -357(lnquired), 125A, 142A; 28l/45(Unofficial); 95/85; 355/3(Domestic); 350/150, 160; 307/262, 262AE [5 6] References Cited UNlTED STATES PATENTS 3,359,469 12/1967 Levy et a1.

2,834,132 5/1958 Taylor et al 317/262 3,448,356 6/1969 Testone .1 317/262 3,282,159 11/1966 Jones et a1. 350/160 3,041,936 7/1962 Hull 350/150 3,473,097 Barnett 317/262 FOREIGN PATENTS 1,040,944 10/1958 Germany 40/142 Primary Examiner-J. D. Miller Assistant Examiner-C. L. Yates Attorney-Stanley Bilker ABSTRACT: A transparent or back-lighted electrostatic copyboard which includes a transparent or translucent nonconductive face plate and a liquid which is conductive at high voltages, such as water, held in abutment with the face plate by a container, also preferably nonconductive and transparent or translucent whereby a unidirectional high voltage applied to the liquid will permit objects to electrostatically adhere to the face plate while being back illuminated therethrough,

BACK LIGHTED ELECTROSTATIC COPYBOARD BRIEF SUMMARY OF THE INVENTION This invention relates to electrostatic copyboards and electrostatic adhesion devices. More particularly, it relates to electrostatic copyholder devices in which objects abutting the mounting surface thereof are illuminated and/or back-lighted therethrough.

Electrostatic copyholder devices are for the most part comprised of a nonconductive front plate to the back surface of which is coupled the hot side of a unidirectional or DC high voltage. Means are generally provided to distribute the high voltage across substantially the entire back surface of the nonconductive plate by means of a large plane electrode so as to most efficiently effect charging of the front face. Abutting fiat objects or sheets against the copyboards face and providing a conductive path return from the object to the other side of the high voltage causes objects to stick to the face with great intensity.

Where it is desirable to illuminate or back light the objects, such as film negatives or x-ray plates, from the rear, a translucent or transparent copyboard plate is utilized and a source of illumination directed from behind, for example, in the manner of a light box. Since an opaque flat electrode on the rear surface of the copyboards transparent front plate would entirely mask and prevent the transmission of light therethrough, two kinds of transparent or semitransparent surface electrodes have been employed in the past.

The first system uses extremely thin evaporative coatings of conductive materials of metals, such as aluminum, gold, nickel, silver, copper and tin. It is readily apparent that conductive coatings are expensive and even when the films were in the thickness range of a wave length of light, they would interfere somewhat with the transmission characteristics, as thin as they are. However, most important of all, the high voltage applied to thin film electrodes causes partial erosion of the conductive film, probably resulting from points or zones of high current density. The ultimate effect which occurs during use is to produce blisters, cracks and peeling, which are not only unsightly, but also result in nonuniform light transmission and discontinuity of electrode surface with consequent interference with electrode surface efficiency.

The other system, mentioned above, previously employed as a back surface electrode, is the abutment of a foraminous sheet electrode, such as a wire mesh screen, against the rearward surface of the face plate of the copyboard. Here, too, it is apparent that the screen mesh has the attendant disadvantages of not only detracting from light transmission qualities and producing shadows on the transparent or translucent plate, but also reducing surface holding efficiency by virtue of the difficulty in obtaining uniform surface contact of all portions of the screen with the rearward face of the copyboard front plate.

It is therefore an object of this invention to provide a transparent or translucent copyboard in which uniform full and complete electrical contact is obtained with the back surface of the copyboard face plate without in any way interfering with light transmission characteristics.

Another object of this invention is to provide a back-lighted electrostatic copyboard in which no erosion of the high voltage electrode occurs.

Yet another object of this invention is to provide a back-illuminated electrostatic copyboard whose color can be easily altered in situ for particular applications.

Still another object of this invention is to provide a transparent electrostatic copyboard in which minimal spurious interfacial reflections will occur.

Yet still another object of this invention is to provide a back-lighted electrostatic copyboard in which shadows are eliminated.

A still further object of this invention is to provide a translucent electrostatic copyboard in which at least two surfaces are available for article pinning.

Yet a further object of this invention is to provide a back-illuminated electrostatic copyholder in which the configuration or shape may be varied infinitely.

Yet still a further object of this invention is to provide a transparent or translucent electrostatic copyholder in which the electrode will not chip, burn, flake, blister, erode nor discolor.

Other objects of this invention are to provide an improved device of the character described which is easily and economically produced, which is sturdy in construction and both highly efficient and effective in operation.

BRIEF DESCRIPTION OF THE FIGURES With the above and related objects in view, this invention consists of the details of construction and combination of parts as will be more fully understood from the following detailed description when read in conjunction with the accompanying drawing in which:

FIG. 1 is a perspective view of a back-illuminated electrostatic copyboard embodying this invention.

'FIG. 2 is a perspective exploded view of the back-illuminated copyboard.

FIG. 3 is a sectional view taken along lines 3-3 of FIG. 1.

DETAILED DESCRIPTION Referring now in greater detail to the drawing in which similar reference characters refer to similar parts, there is shown a back-illuminated or translucent electrostatic copyboard comprising a translucent front plate, generally designated as A, a translucent back plate, generally designated as B, a transparent liquid C which is relatively conductive at high voltages encapsulated therebetween, and a unidirectional or DC high voltage power supply D whose hot side is connected to the liquid C.

The term translucent" is intended to generically encompass the quality or property of being completely transparent as well as being semitransparent or semiopaque. For example, the front plate A may be transparent while the back plate B may be partially transparent to light transmission whereby the user may at his discretion elect either of the two alternatives as the pinning surface. It is preferable that the plates A and B are glass, which is nonconductive and has a resistivity in the range of 10 to 10'] ohm centimeters. While the face plates A and B are shown as flat and rectangular in configuration, there is no reason why any other external shape cannot be employed, for example, partially cylindrical or spheroidal.

As shown, the liquid C is encapsulated in between the two face plates A and B. An annular rectangular electrode 12 is centrally disposed between the two plates A and B. The electrode 12 is desirably made from stainless steel because of its low electromotive activity and high corrosion resistance. A peripheral gasket 14 of suitable elastomeric material, such as a silicone rubber composition, acts both as a high voltage insulator and as a seal for the liquid. The liquid C is preferably distilled water which has the desired pH of 7 and a volume resistivity of 63 megohm centimeters. The advantages of distilled water are its low ionization constant, its having an index of refraction almost exactly that of glass, and its purity which would prevent plating out of dissolved salts as would happen in the case of tap water or other electrolytes. In view of the fact that the current carrying capacity of the high voltage liquid electrode need only be in the range of a few microamperes, the low current capacity of distilled water will be sufficient in this situation.

A fill tube 16 with a suitable cap 18 is mounted and sealed within an opening at the top of the back face plate B to permit the liquid C to be incorporated between the two plates A and B. Similarly, a drain port 20 with a suitable plug 22 or valve enables the liquid to be emptied from the encapsulating receptacle. Vent tube 24 or breather allows the gas bubbles to exit and permit filling of the liquid without trapping large volumes of air. The liquid C may also be colored.

The high voltage power supply D may be any appropriate high voltage, low current DC generator having a capacity of perhaps 5,000 to 20,000 volts DC and a current of approximately 25 microamperes. it is preferable that the generator D be operated negatively on the hot side so that a negative voltage will be coupled to the annular electrode 12 in contact with the liquid. A sealed lead 26 extending through the back plate B is connected to the electrode 12. The operation of the liquid, water or electrolyte, at a negative voltage is advantageous in order to prevent any metal ions, which are positive, from plating out from the electrode 12 into the liquid. Thus, only the negative silicon from the glass will plate out into the electrolyte liquid, and the silicon in these concentrations will dissolve in the liquid.

When the DC high voltage is applied to the liquid electrode C, an object 30, such as a sheet of film or paper placed in abutment with the front surface A will slightly adhere thereto. This electrostatic adhesion is improved by grounding the entire back surface of the object so that a conductive path from the back surface of the object to the other side of the high voltage power supply will permit charges of the opposite polarity, in this case positive, to accumulate on the object 30 in juxtaposition with the negatively charged face plate A. The theory of electrostatic adhesion is set forth in detail in prior US. Pat. No. 3,359,469. A bulb 32, which is representative of either a battery of incandescent or fluorescent lamps or even sunlight, clearly back illuminates the front transparent face plate A to permit inspection or exposure of such objects as film or x-rays preparatory to composition or to photographic printing. The light 32 can be reversed to back illuminate the face plate B where it is semiopaque. It is also possible to edge light the liquid C by suitable projection through the margins of the gasket 14. Moreover, the configuration of the entire copyboard may be cubic or boxlike in configuration with five or six different face plates of desired opacity, under which circumstances, the illumination means 32 can be internally mounted. With the liquid electrode C, there is no limit as to the configuration of the face surfaces, for example, a liquid inflated balloon under the circumstances could be adapted for electrostatic copyboard applications. It is also possible to utilize completely opaque plates with a liquid conductor, even mercury being adaptable for this application.

Although this invention has been described in considerable detail, such description is intended as being illustrative rather than limiting since the invention may be variously embodied,

and the scope of the invention is to be determined as claimed.

Iclaim:

1. An electrostatic copyboard for illuminating articles from behind comprising an electrically nonconductive translucent face member having surfaces, a fluid container mounted behind said face member, a transparent high voltage conductive liquid in said container and in abutment with one of the sur faces of said face member, means for applying one side of a unidirectional high voltage to said liquid, and means for applying the other side of said unidirectional high voltage to a nonliquid-contacting surface of said face member whereby an object placed against the nonliquid-contacting surface of said face member can be made to electrostatically adhere thereto.

2. The copyboard of claim 1 wherein said container includes a second translucent electrically nonconductive face member.

3. The copyboard of claim 2 wherein said face members are adjacently spaced from each other.

4. The copyboard of claim 3 wherein said face members are glass.

5. The copyboard of claim 3 wherein said face members are each glass, one being transparent and the other semiopaque whereby objects can adhere to either and be illuminated through the other.

6. The copyboard of claim 3 wherein said liquid is water.

7. The copyboard of claim 6 wherein the water is distilled.

8. The copyboard of claim 1 wherein the one side of the high voltage connected to the liquid is negative.

. The copyboard of claim 6 wherein said means for applying a unidirectional high voltage constitutes a stainless steel plate of annular configuration forming an electrode in the water.

10. The copyboard of claim 3 wherein the plates are vertically disposed.

11. The copyboard of claim 10 including a filler tube at the upper portion of one of said plates to add liquid, a drain tube at the lower portion, and a breather at the upper portion to release gas bubbles.

12. In an electrostatic copyboard, an electrically nonconductive face member having opposite surfaces, an electrically conductive liquid in contact with one surface of said face member, and means for applying one side of a unidirectional high voltage to said liquid and means for applying the other side of the unidirectional high voltage to the nonliquid-contacting surface of the face member. 

